GLACIAL EROSION IN ALASKA 113 



the grade of this valley out into the main trough of Disenchantment 

 Bay, where the nearest soundings show a depth of from 600 to 1,000 

 feet, the profile falls far short of reaching the bed of the bay. It is 

 assumed, therefore, to be a hanging valley with the lip at or just 

 below the surface of the fiord water. If we grant that this particular 

 hanging valley may be due to faulting, which can not be disproved, 

 we are still left with the necessity of assuming block faulting along 

 the axis of the Eussell Valley to account for the hanging condition of 

 its own tributaries whose lips lie fully a thousand feet above the Eussell 

 Valley bottom (Fig. 12). In some cases even a third series of laterals 

 have been seen hanging above a tributary, which itself hangs above 

 another, which is hanging above a main trough. 



To propose faulting as an explanation for such a complex system 

 of hanging valleys does not seem rational without definite evidence 

 of the faulting, and without some explanation of why the results of 

 such recent faulting are so common in glaciated regions and so rare in 

 unglaciated areas. Moreover, in some of the cases mentioned, for ex- 

 ample, the Eussell Valley itself, if there had been such faulting, it 

 would be easily detected in the sedimentary rocks which form the walls 

 of the valley. Since a search for evidence of recent faulting in this 

 valley failed to find it, I feel warranted in asserting that there has been 

 no such faulting as the theory demands. A glance at the photographs 

 (Figs. 10 and 11) is sufficient to show that the form of this valley 

 could not be accounted for on the basis of block faulting. Its flaring, 

 curving, U-shaped sides are not the forms characteristic of cliffs due 

 to faulting. Should it be stated that block faulting occurred at a 

 date sufficiently remote to permit the weathering back of the valley 

 walls to the present curve, it is sufficient to answer that in all the 

 time required for this, the lateral streams must of necessity have 

 trenched the bottoms of the hanging valleys and reduced them to an 

 accordant grade with the Eussell Valley stream. As Fig. 12 clearly 

 shows, this is far from being the case. 



From the above statement of hypotheses it will be seen that it 

 is generally admitted that hanging valleys are a peculiar phenomenon 

 calling for special explanation. It is also true that this phenomenon 

 is practically confined to regions of former glaciation. Together with 

 the U-shaped valle} r , truncated spurs, and steepened main valley slopes, 

 the condition of hanging valleys is reported not only from a wide area 

 in Alaska and British Columbia, but in such other regions of former 

 glaciation as the Sierra Nevada, the Eocky Mountains, the Finger 

 Lake Valleys of central New York, the coast of Norway, the Alps, 

 the Himalayas and New Zealand. While exceptional instances of 

 hanging valleys, which are readily explained in other ways, have been 

 reported from unglaciated regions, these are so few and scattered, and 

 VOL. lxx. — 8. 



